The common industrial pallet is made of wood. It is provided with similar top and bottom continuous or slatted surfaces, spaced apart by wooden blocks, elongated wooden spacers/reinforcements and side walls to provide a gap of appropriate size therebetween, to give access to the lifting forks of a forklift truck from two or four sides. Such pallets should be robust and rugged in construction, to withstand the weight of goods stacked on them and lifted on top of them, and to withstand the impacts of truck forks driven into them as a result of misalignment. They are commonly made in a variety of different shapes and sizes. They may be nailed, screwed or riveted together, using the particular design and choice of wood appropriate for their particular use and the loads they are intended to carry.
Such wooden pallets, in particular those made of softwood, are disposable, one-way items. They are sufficiently cheap in terms of raw materials and manufacturing costs, and also sufficiently heavy and bulky, that their return transportation when empty is not economic. However, they are prone to damage in use, and on exposure to weather. In addition, many manufacturing environments do not tolerate wood dust or loose splinters, nails, rivets etc. Since in addition such pallets pose significant disposal problems, there are legislative moves to reduce or eliminate their use.
Reusable, returnable industrial pallets are also known. These are normally made of thermoplastics or thermosetting materials, by processes of injection molding or compression molding. These processes of manufacture require relatively high investment in both tooling and machinery. Moreover, the high cost for the plastics raw materials contribute to the relatively high overall cost of such pallets.
Friction welding, e.g. spin welding, vibration welding etc., is a technique which has previously been used, in one industrial area, to form permanent connections between lengths of thermoplastic pipe, by rotating one or both ends of the pipes under pressure against each other. It has also been used, in another industrial area, to weld the thermoplastic reinforcement of an automobile bumper into the thermoplastic front fascia by vibrating both surfaces under pressure against each other. It relies upon the heat generated by friction in the relative movement of one surface relative to another, under conditions of pressure contact between the respective surfaces. As a result, the thermoplastic material of one or both of the surfaces melts, and on cooling, a union is formed with the thermoplastic material of the other surface, to form a thermoplastic weld on cooling.
It is an object of the present invention to provide novel returnable industrial pallets.
It is a further object to provide an economical process for producing such pallets and other similar industrial structures, so that the resulting products are relatively cheap but at the same time strong and durable.